This invention relates to nondestructive testing of bodies or objects by magnetic particle inspection procedure, for detection of defects and metallurgical conditions, particularly in the surface of the body, and is particularly concerned with a simple method for facile and rapid magnetic particle inspection of bodies by employing a viewing device, perferably containing weakly magnetic crystals, in conjunction with a novel magnetic recording medium of a type having properties permitting it to conform to complex surface configurations of an object, and wherein magnetic indications of defects, discontinuities and varying metallurgical conditions in the object are first recorded on such recording medium, said viewing device permitting visual observation with clarity and sharpness, of such magnetically recorded magnetic indications.
Conventional magnetic particle inspection methods for nondestructive testing of bodies generally employ solutions or powders of magnetic material such as ferromagnetic oxides, which are applied to the surface of the object and build up over cracks or defects contained in bodies of magnetic materials such as steel. In these methods the magnetic particles generally are directly deposited over the surface of the objects or parts, contaminating them. Such magnetic particles are used up in the process and they are generally not recoverable since they attach or adhere to the magnetized surface of the parts being inspected. Thus, the magnetic particles in these methods contaminate the surface of the objects being inspected. Further in these conventional methods for nondestructive flaw and crack detection, the magnetic flux applied to the object must be induced at right angles to the suspected cracks and defects for satisfactory results.
An improved method for magnetic inspection of parts is disclosed and claimed in my copending U.S. application Ser. No. 360,988 filed May 16, 1973 now U.S. Pat. No. 3,855,526. According to the latter application, a contrasting, e.g. white, background coating is applied over the surface of the object or part to be inspected, a field of magnetic flux lines is established relative to the object, and magnetic particles, preferably suspended in a suitable liquid medium, are applied over the coating, the field of magnetic flux lines causing the magnetic particles to agglomerate on the coating over the surface defects and discontinuities, and the body is inspected to reveal the defects and discontinuities as defined by the magnetic particle indications produced by the agglomerated magnetic particles.
Although the above procedure of my copending application is effective and advantageous, there is disclosed in my copending application Ser. No. 420,326, filed Nov. 29, 1973, novel magnetic inspection procedure employing a magnetic recording medium such as magnetic tape for recording magnetic indications of defects and discontinuities in the object, in conjunction with a relatively simple viewing device for viewing the outline of such defects and discontinuities corresponding to the magnetic indications thereof in such recording medium. Such procedure permits effective and rapid detection of surface cracks, flaws, discontinuities and varying metallurgical conditions, with high sensitivity, without at all contacting or contaminating the part surface with magnetic particles.
However, although the use of a magnetic recording medium such as magnetic tape in the procedure of my above copending application permits magnetic inspection of objects or parts having an irregular shape, in many instances it is necessary to inspect more complex configurations including holes, threaded areas, and sharp curvatures in objects. This is difficult to accomplish employing magnetic tape as the recording medium according to the procedure of my above copending application.
It is accordingly a particular object of the present invention to provide a novel magnetic inspection procedure employing a viewing device of the type disclosed in my above copending application Ser. No. 420,326, but including means for initially recording magnetic indications of defects and discontinuities and metallurgical conditions in a part, in the form of a magnetizable material which when applied to a part having complex configurations such as, for example, highly irregular surfaces, large cracks, holes, threaded areas and sharp curves, readily conforms to the shape of such configuration, and then viewing such recorded magnetic information in such viewing device applied to such magnetic medium, to obtain visual indications of such previously recorded indications of the surface cracks, flaws and discontinuities, and metallurgical conditions in the object or part, with a sharpness and clarity equal to that obtained when a magnetic tape is employed, in accordance with the method of my above last-mentioned copending application. Another object is the provision of a novel magnetic recording medium for use in the above method.